The present invention relates, in general, to a linear motor, and more particularly to a linear motor of polygonal cross section. The present invention further relates to a method of making a linear motor.
In this application, the term “polygonal” is not limited to a closed plane figure bounded by straight lines, but should be construed to also encompass shapes with curved or rounded corners.
Linear motors of a type involved here include typically a primary, which is comprised of several lamination stacks so arranged as to form a polygon structure, and a secondary having permanent magnets to generate a magnetic field. Mechanical engineering and plant construction increasingly use linear motors as electric direct drives because of the attainable control dynamics, high positional accuracy, attainable accelerations and speeds as well as long travel paths. The primary has current-carrying coils to generate a variable magnetic field which in cooperation with the magnetic field of the secondary causes a movement of the primary in relation to the secondary. More and more, there is a demand for further increase in the thrust force.
One approach to address this demand involves the construction of a double-sided linear motor through addition of a second primary to a single-sided linear motor so as to realize a doubling of the thrust force. Another approach is described in European patent publication EP 0 744 815 which discloses a polygonal linear motor. The linear motor has a primary which is surrounded by a secondary having permanent magnets which are disposed on a carrier of polygonal cross section. The primary has a retention arm which extends through a gap of the carrier for the secondary to the outside for connection to a linear guide.
However, for a number of reasons, the various proposals are endowed with drawbacks and shortcomings relating for example to manufacturing techniques or to the effect that is hoped to be obtained but may not always be realized.
It would therefore be desirable and advantageous to provide an improved linear motor which obviates prior art shortcomings and which is simple in structure and compact which still producing high power output and which allows modification in a simple and cost-efficient manner in order to cover a wide power range.